Congestive heart failure (CHF) is a condition that affects millions of people worldwide. CHF results from a weakening or stiffening of the heart muscle that commonly is caused by myocardial ischemia (due to, e.g., myocardial infarction) or cardiomyopathy (e.g., myocarditis, amyloidosis). CHF causes a reduced cardiac output and inadequate blood to meet the needs of body tissues.
Treatments for CHF include: (1) pharmacological treatments, (2) assisting systems, and (3) surgical treatments. Pharmacological treatments, e.g., with diuretics, are used to reduce the workload of a heart by reducing blood volume and preload. While pharmacological treatments can improve quality of life, they have little effect on survival. Assisting devices, e.g., mechanical pumps, are used to reduce the load on a heart by performing all or part of the pumping function normally done by the heart. However, in a chronic ischemic heart, high-rate pacing may lead to an increased diastolic pressure, calcium overload, and damages to the muscle fibers. There are at least three surgical procedures for treating a heart failure: (1) heart transplant, (2) dynamic cardiomyoplasty, and (3) the Batista partial left ventriculectomy. These surgical treatments are invasive and have many limitations.
CHF is generally classified into systolic heart failure (SHF) or diastolic heart failure (DHF). In SHF, the pumping action of a heart is reduced or weakened. A normal ejection fraction (EF), the volume of blood ejected out of the left ventricle (stroke volume) divided by the maximum volume remaining in the left ventricle at the end of the diastole or relaxation phase, is greater than 50%. In a systolic heart failure, EF is decreased to less than 50%. A patient with SHF may have an enlarged left ventricle because of cardiac remodeling developed to maintain an adequate stroke-volume. This pathophysiological phenomenon is often associated with an increased atrial pressure and an increased left ventricular filling pressure.
DHF is a heart failure without any major valve disease even though the systolic function of the left ventricle is preserved. Generally, DHF is a failure of the ventricle to adequately relax and expand, resulting in a decrease in the stroke volume of the heart. Presently, there are very few treatment options for patients suffering from DHF. DHF afflicts between 30% and 70% of patients with CHF.
Devices to treat elevated left atrial pressure have been described. For example, U.S. Pat. Nos. 8,740,962 and 8,460,372 both describe prostheses that may be implanted in an opening in the septal wall of the heart to provide a shunt or channel permitting blood to flow from the left atrium into the right atrium. These devices collapse to a smaller configuration for delivery to the heart via a catheter and expand to a larger configuration (e.g., through self-expansion) upon deployment across an opening in the septal wall. Some of these devices have central cores with sufficient radial strength to maintain the patency of the septal wall opening and flexible anchors on both sides of the central core to contact the septal wall for atraumatic anchoring of the device. Some of these devices have retrieval legs and other features providing attachment points for delivery and/or retrieval for possible removal or redeployment.